Arithmetic calculation (8)
I believe the answer is:
addition
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">arithmetic calculation</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for addition that I've seen before include "Arithmetic calculation" , "Reckoning" , "Rider" , "Mathematical process" , "Process of summation" .)